If you mean varnish then paint on top of that, I'm not sure as I've never tried it. Acrylic varnish on top of acrylic paint? Yes, it will (although to qualify that, it may be that it just bled through the paint, but as the varnish was clear, then you could obviously see it. So it may not have actually bled through the varnish) I rarely use enamels these days, so don't know how badly they would be affected, but marker pens do bleed through Halfords primer & top coats, as we found out when working on the inside of our Mini!
That signal box looks brilliant....!!
Keith